1. Field of the Invention
The present invention relates to a differential pressure transmitter (pressure detector) and a method of diagnosing blockage of impulse lines which are connected with a high pressure side and a low pressure side by using a differential pressure signal and a static pressure signal. Particularly, the present invention relates to a differential pressure transmitter (pressure detector) and a method of diagnosing blockage of impulse lines of a high pressure side and a low pressure side respectively.
2. Description of the Related Art
There is a related differential pressure transmitter (pressure transmitter) for generating and transmitting a differential pressure signal and a static pressure signal from a high side pressure and a low side pressure, and detecting a blockage state of one or both of impulse lines from a correlation between a fluctuation of the differential pressure signal and a fluctuation of the static pressure signal (refer to, for example, JP-A-2004-132817). Further, a result of diagnosing the blockage is transmitted by a predetermined method.
However, the related differential pressure transmitter has a problem that blockage of only a high pressure side impulse line and blockage of only a low pressure side impulse line cannot be diagnosed.
With regard to such a problem, according to JP-A-2005-274501, blockage of a high pressure side impulse line and blockage of a low pressure side impulse line can simply and accurately be diagnosed.
Further, the fluctuation of pressure is influenced by a flow rate of a process, and therefore, a problem arises that it is difficult to diagnose blockage of the impulse lines.
In details, when the flow rate of the process is small, a value of an fluctuation of a pressure tends to be small. Therefore, it is difficult to determine whether the value of the fluctuation of the pressure is small since the impulse line is blocked, or the value of the fluctuation of the pressure is small since the flow rate of process is small.
Therefore, according to the related differential pressure transmitter, a reference value for diagnosing blockage is switched at each time of setting the flow rate of the process. Therefore, according to the related differential pressure transmitter, it is necessary to change the reference of diagnosing blockage in accordance with a value of the flow rate of the process, and thus a problem arises that maintenance cost is required.